Gamma Ray Irradiation Effects on Electrical Transport and Microwave Properties of BISCO Superconducting Films

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High-Tc Superconducting films of Bi–Sr–Ca–Cu–O (2:2:1:2) have been synthesized by spray pyrolysis of nitrate precursors onto yttria stabilized zirconia (YSZ). γ-ray irradiation of the sample, was carried out using a 60Co source of 103 Ci strength for several hundreds of hours; the dose received by the samples was 80 K rad/hr. Superconducting properties such as critical transition temperature (Tc), resistivity (R), critical current density (Jtc). Voltage-time relaxation (Vt) and microwave induced dc voltage were investigated as a function of temperature down to 77 K after γ-ray irradiation. γ-ray irradiation was found to have practically no effect on its structural modification and on the critical transition temperature. However, transport critical current density (Jtc) increased. The increase of pinning energies with irradiation suggests that these changes in properties are dominated by radiation-induced randomly distributed mobile oxygen defects in the films. An appreciable decrease in the microwave-induced dc voltage at 77 K was also observed after irradiation which suggests that the mobile defects are clustered at the major defect region and reduce the total number of weak links. These results suggests that oxygen defects induced by γ-ray irradiation of BISCO films act as important and major pinning centers which is responsible for the enhancement of Jtc and reduction of microwave induced dc voltage.

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